The present application relates to a display device that includes a light sensor in a display pixel part or on the frame of the display pixel part, and electronic apparatus.
A technique is known in which the illuminance of ambient light is detected by a photo sensor to thereby increase the screen luminance when the ambient illuminance is high and decrease the screen luminance when the ambient illuminance is low. The visibility of the screen is enhanced by using this technique. In addition, if images are displayed by using a backlight system, such as one in a liquid crystal display device, the power consumption of the backlight system is reduced by this technique, which can contribute to extension of the life of a battery in mobile applications such as cellular phones. Thus, various studies are being made on this kind of technique.
Furthermore, several techniques in which a display device itself is provided with a coordinate input function have been proposed.
Specifically, e.g. display devices based on a pressure-sensitive touch panel system (refer to Japanese Patent Laid-Open No. 2002-149085 and Japanese Patent Laid-Open No. 2002-41244), and display devices based on an electromagnetic-induction touch panel system (refer to Japanese Patent Laid-Open No. Hei 11-134105) are known.
However, these display devices with the coordinate input function involve a problem that size reduction thereof is difficult and the cost thereof is higher than that of general display devices.
To address this problem, in recent years, a display device is being actively developed in which each pixel is provided with a light-receiving element and incident light on the light-receiving element is detected to thereby specify coordinates in the display device (refer to Japanese Patent Laid-Open No. 2004-318067 and Japanese Patent Laid-Open No. 2004-318819).
This device, in which the light-receiving element is provided to thereby allow coordinate input in the display device, has advantages over the display device having the coordinate input function in that size reduction is possible and the cost can also be reduced. In addition, this device allows multiple-coordinate input and area input.
However, as shown in FIG. 1, a photo sensor has sensitivity to the near-infrared region as well as to visible light.
Therefore, the photo sensor detects light in the near-infrared region e.g. under an incandescent light bulb, which provides ambient light involving infrared light. Consequently, even under an environment in which the illuminance is not very high in fact, the photo sensor reacts as if this environment had comparatively-high illuminance, which results in a large error in the evaluation of the ambient illuminance.
Therefore, in order to evaluate merely the illuminance of the visible region, an infrared-cut filter needs to be mounted in front of the sensor separately.
As this infrared-cut filter, a dielectric filter obtained by coating glass with multiple layers of an inorganic film or a filter coated with a dye that absorbs light in the infrared region is used in general.
However, in the case of fabricating the filter on the periphery of the display area of a display device and attaching the filter to the sensor part separately, the filter needs to be mounted with the intermediary of some degree of distance from the display area in order to avoid interference with the display area. This distance leads to an error in measurement of the screen illuminance.
Moreover, because the filter is provided separately, the number of components is increased and the manufacturing process becomes complex, which leads also to cost increase.
If a film such as a polarizer is used for displaying like in a liquid crystal display device, a method would also be available in which the infrared-cut filter is provided integrally with this film to thereby reduce the number of components and dispose the photo sensor close to the display area. However, because the infrared-cut filter itself is colored, the display quality itself is adversely affected, which makes it difficult to employ this method.
In addition, there is a disadvantage that noise of reflected light inside the display device may not be removed in real time in the above-described system and a system for realizing a touch panel, an image sensor, and so on by utilizing light that originates from a backlight and is reflected from a detection subject such as a finger.
Moreover, interference noise from the display part may not be removed in real time in the above-described system based on light from a backlight and an imaging system based on ambient light.
Furthermore, for these reasons, a highly-reliable system that has a favorable temperature characteristic and is robust to temporal variation may not be achieved.
In addition, to achieve the highly-reliable system, calibration operation at the time of power activation is desired.